1. Field of the Invention
The present invention relates to a lens barrel which is mounted onto a camera body, and, more particularly, the present invention relates to a lens barrel having an iris stop unit having a support ring, blades and a drive ring, wherein the blades and the drive ring are secured to the d support ring using a lens group holding frame.
2. Description of the Related Art
Various types of lens barrels which are mountable on a camera body are known. The known types of lens barrels which are mountable on a camera body include single-focal-length lenses and zoom lenses ranging from wide-angle lenses to telephoto lenses. A lens barrel having a plurality of lens groups, which comprise one or multiple optical lens elements, can obtain accurate focusing by varying the relative distance between each lens group. Moreover, a type of lens barrel is known which incorporates exposure and depth of focus control in the lens barrel, and includes an aperture stop device built into the lens barrel to control the volume of light flux. Presently, the most prevailing aperture stop device is an iris stop unit which consists of a plurality of blades arranged diametrally. The iris stop unit controls a numerical aperture by moving the plurality of blades.
The conventional iris stop unit includes several blades, a support ring which supports the blades in a freely pivotable manner, and a drive ring having a cam which makes the blades pivot. The blades are pivoted by rotating the drive ring. The drive ring may be rotated by manually rotating an aperture ring arranged in an external surface of the lens barrel. However, in autofocus lens barrels, the drive ring is rotated by the drive control system of a camera body through an aperture stop coupling lever.
The conventional iris stop unit is fixed to a lens group holding frame (fixed tube or moving tube) using a fixing ring having a male screw on its external surface, or using a fixing ring having a perforated hole. The support ring of the iris stop unit may either be separated from the supporting parts for the lens group holding frame, or built onto the supporting parts for the lens group holding frame.
The conventional lens barrel which uses a fixing ring to fix an iris stop unit results in the problems of increased process time and an increased number of parts. For example, when a fixing ring with a male screw cut on its external surface is used to secure the iris stop unit, a female screw must be cut on the internal surface of the supporting parts for the lens group holding frame. Further, a special tool is required to turn the fixing ring around. Furthermore, if the fixing ring with a perforated hole is used to secure the iris stop unit, it becomes necessary not only to bore a threaded hole, but also to fasten multiple (nonnally more than three) screws with a screw driver. Thus, the number of parts and the process time required to fix the iris stop unit increases.